Male
Erection

How it develops — and what influences it

An erection is not a simple reflex. It is the result of a precise interplay of the nervous system, hormones, blood vessels, and psyche — in which many things have to be right at the same time. Those who understand how an erection works also better understand why it sometimes doesn't function as desired — and what can be done about it.

This page explains the physiology of the male erection in an understandable way, without jargon — as a foundation for an informed approach to one's own body.

The Anatomy: What happens in the penis?

The penis contains three cylindrical erectile bodies:

Two corpora cavernosa (penile erectile bodies) — run side by side through the entire penile shaft and are primarily responsible for the erection
One corpus spongiosum — surrounds the urethra and forms the glans; prevents the urethra from kinking during erection

The erectile bodies consist of a sponge-like network of smooth muscle tissue and small blood vessels — the so-called lacunae. In a relaxed state, these vessels are narrow, and blood flow is minimal. During sexual arousal, this changes fundamentally.

Anatomy at a glance

Corpora cavernosa: Two parallel erectile bodies — primarily responsible for the erection
Corpus spongiosum: Surrounds the urethra · forms the glans · prevents kinking
Tunica albuginea: Stable connective tissue sheath around the erectile bodies — enables pressure buildup
Vascular network (lacunae): Microscopic blood vessels in the erectile tissue — fill up during arousal

The Physiology: How an erection develops — step by step

An erection proceeds in clearly defined phases — triggered by the nervous system, controlled by messenger substances, and made possible by the anatomy of the erectile bodies:

Phase	What happens in the body
1. Stimulus & Signal	Sexual arousal (visual, tactile, mental, or through smell) activates the parasympathetic nervous system in the sacral spinal cord (S2–S4). Nerve endings in the penis release the messenger substance nitric oxide (NO).
2. Vasodilation	NO activates the enzyme guanylate cyclase in the vessel walls → cGMP is formed → the smooth muscle of the erectile body vessels relaxes → arteries dilate.
3. Blood inflow	Through the dilated arteries, blood flows under high pressure into the lacunae of the corpora cavernosa — the volume increases sharply.
4. Venous compression	The filled erectile bodies press the outflow veins (venules) against the rigid tunica albuginea — the blood outflow is throttled. The pressure continues to rise.
5. Full erection	The internal pressure of the erectile bodies rises to 80–100 mmHg. The penis is fully erect and firm.
6. Detumescence (subsiding)	After orgasm or when arousal diminishes, the enzyme PDE-5 breaks down cGMP → vessels contract → blood flows out → erectile bodies relax.

This entire process typically takes 10–30 seconds from arousal to full erection — when all systems work together smoothly.

The role of testosterone in the erection

Testosterone is not directly responsible for the mechanical process of the erection — but it is an essential prerequisite for the system to function optimally.

Stimulates nitric oxide (NO) synthesis in the erectile bodies — the crucial messenger substance of the erection
Maintains the health of the erectile tissue — low levels promote fibrosis and tissue loss
Regulates libido and sexual desire in the brain — without desire no arousal, without arousal no erection
Influences the sensitivity of the nerves in the penis
Protects the endothelial function of the blood vessels — important for the vasodilation response

This is why andropause and erection problems so often go hand in hand. A testosterone deficiency does not weaken a single function — it impairs the entire system.

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What influences the erection —
positively and negatively

Erectile function is not a fixed value — it is a dynamic system that depends on many factors. Some of them are within a man's control, others are not.

Influencing factor	Positive effect (promotes)	Negative effect (inhibits)
Testosterone	Sufficient level promotes NO synthesis, libido, and tissue health	Deficiency weakens all three erection components simultaneously
Cardiovascular system	Healthy vessels, good circulation, normal blood pressure	Arteriosclerosis, high blood pressure, diabetes: all narrow the erectile body vessels
Nervous system	Intact parasympathetic nerves (sacral spinal cord, pelvic floor)	Nerve damage due to diabetes, spinal cord injuries, prostate surgery
Psyche	Relaxation, sexual confidence, positive body image	Performance pressure, anxiety, depression, stress increase adrenaline → inhibits erection
Sleep	Sufficient sleep secures testosterone and regeneration	Sleep deprivation and apnea lower testosterone and impair vascular function
Exercise	Endurance training improves endothelial function and circulation	Lack of exercise promotes obesity, insulin resistance, vascular changes
Nutrition	Mediterranean diet, zinc, omega-3 promote vascular and hormonal health	Sugar, trans fats, obesity increase inflammation markers and estrogen
Alcohol	In small amounts socially relaxing (short-term)	Chronic consumption damages nerves, lowers testosterone, impairs NO synthesis
Medications	Few medications actively promote the erection	Antidepressants, beta-blockers, diuretics, antiandrogens can inhibit erection

Important: Occasional erection problems — e.g. due to stress, exhaustion, or after alcohol — are completely normal and have no disease value. Only when problems occur regularly or are distressing is a medical evaluation advisable.

Three types of erection —
and what that says about your health

Not every erection develops the same way. Medicine distinguishes three types — and each gives the doctor important clues:

Psychogenic erection

Triggered by sexual imagination, images, fantasies, or stimuli. Runs via the cerebrum → spinal cord → parasympathetic nerves. Psychological factors such as anxiety or performance pressure can disrupt it — even with completely intact physical function.

Reflexogenic erection

Triggered by direct physical touch of the penis or the genital region. Runs via local reflex arcs in the sacral spinal cord — independent of consciousness. This type of erection can also be preserved in cases of paraplegia above the sacral spinal cord.

Nocturnal / morning erection (NPT)

During REM sleep, 3–5 erections occur automatically per night — independent of sexual arousal. They serve to supply oxygen to the erectile tissue and are an important sign of healthy vascular and nerve function. The doctor asks specifically about this: Absent morning erections are a clinical indication of an organic cause of erection problems.

Clinical note: Morning erections

Regular morning erections = blood vessels and nerves are functioning — erection problem more likely psychological.

Absent morning erections = possible organic finding — vascular, nerve, or hormonal disorder likely.

This distinction is one of the first questions in the medical consultation regarding erection problems.

When is a medical evaluation advisable?

Many men wait too long — out of shame, out of uncertainty, or because they hope it will get better on its own. Yet erectile dysfunction is a highly treatable condition. And it is sometimes an early warning sign of more serious diseases.

A medical evaluation is recommended if:

Erection problems occur in more than half of attempts
They persist for more than 3 months
Morning erections have become significantly less frequent or weaker
Libido has noticeably decreased
Additional symptoms such as exhaustion, low moods, or weight gain arise
Risk factors are present: diabetes, high blood pressure, smoking, obesity

Erectile dysfunction can be one of the first signs of a heart disease or arteriosclerosis — because the small penile arteries react to vascular changes earlier than the large coronary vessels. Anyone who has erection problems should therefore always also know their cardiovascular status.

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Frequently asked questions about shockwave therapy

How many erections per night are normal?

Healthy men have 3–5 nocturnal erections per night, each of which can last 20–40 minutes. These decrease slightly with age but should still occur regularly even in men over 60. They serve to supply oxygen to the erectile tissue.

Why do erections sometimes fail despite sexual arousal?

Because an erection is a complex interplay — and stress, performance pressure, or anxiety activate the sympathetic nervous system. Adrenaline narrows the vessels and inhibits exactly the mechanism needed for the erection. This is not a weakness, but a neurophysiological reaction — and highly treatable.

Does penis length affect erectile function?

No. Erectile function depends on vascular, nerve, and hormonal health — not on anatomical measurements. Even men who are dissatisfied with their anatomy can have completely normal erectile function.

Can medications affect erections?

Yes — some commonly prescribed medications have erectile dysfunction as a side effect: certain antidepressants (SSRIs), beta-blockers, blood pressure medications (thiazides), antiandrogens, and some stomach medications. Actively raise this with your treating physician — there are often well-tolerated alternatives.

What is the difference between an erection problem and erectile dysfunction?

Occasional erection problems are normal — every man experiences them. One speaks of erectile dysfunction (ED) when the inability to achieve or maintain an erection sufficient for sexual intercourse persists for at least 3 months and occurs in more than half of attempts. Only then is a medical diagnosis and treatment indicated.

Questions about erectile function?

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About the author

Dr. med. Timo A. Spanholtz
Specialist in Plastic and Aesthetic Surgery - Specialist in Men's Health and Intimate Surgery

Dr. Spanholtz is the founder and chief physician of the AndroKlinik. With many years of clinical experience in men's health, andrology, and reconstructive urology, he accompanies patients from the entire German-speaking region.

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Male
Erection

How it develops — and what influences it

The Anatomy: What happens in the penis?

Anatomy at a glance